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helijohn
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Joined: 24 Nov 2003
Posts: 2612
Location: Seaside resort
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 Posted: Sun May 17, 2015 15:25 Post subject: |
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| peteinchad wrote: |
... and the gauge is working.
I wonder whether the PTFE tape is insulating the sender from the block so you are not getting a circuit.. |
Before I installed it I tried connecting a wire to earth to it (the new sender) and it didn't register. Had I put the electric paint stripper nozzle on it maybe it would have registered. I also put the PTFE high up so the starter threads were exposed.
It registers the same reading as the old sender but when the engine is warm; the needle comes up to the lowest mark the gauge has which is about a tenth up the scale.
So if it moves it must have electrical continuity do we think.
I was wondering if there is overcooling as in when the thermostat is wide open or not even present but I checked circulation and it behaves like the thermostat is present and working. |
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| Posted: Sun May 17, 2015 15:25 Post subject: Google Ads keep the POCUK free to join! |
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peteinchad
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Joined: 07 Jan 2013
Posts: 15079
Location: UK
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| Posted: Sun May 17, 2015 18:58 Post subject: |
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It's not likely that you have got two duff senders.
Have you got a multimeter to read the resistance of them?
Usually the resistance is high when cold and gets lower when they get hot. So if you try the old one in a cup of boiling water and watch what happens as it cools down.
Maybe your gauge is going to the top of the scale when you short the wire to earth - but not very sensitive to low resistances. ... I'm clutching at straws with that idea though.
The only way to check if the engine is too cold is to fit an aftermarket temperature gauge with a sender in the top radiator hose. Lots of people do that on the bigger trucks because the OEM gauge is not very accurate anyway.
I fitted an extra gauge and when it showed me my engine wasn't running too cold then I changed the original sender only because I don't like things that don't work properly. Even though my OEM gauge is working now, I never look at it and use the aftermarket one. |
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helijohn
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Joined: 24 Nov 2003
Posts: 2612
Location: Seaside resort
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| Posted: Sun May 17, 2015 19:31 Post subject: |
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| peteinchad wrote: |
It's not likely that you have got two duff senders.
The only way to check if the engine is too cold is to fit an aftermarket temperature gauge with a sender in the top radiator hose. Lots of people do that on the bigger trucks because the OEM gauge is not very accurate anyway.
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Great minds think alike.  
I've been looking at accessory gauges, possibly with a sender with the same thread even.
I've had a lot of replacement parts over the years that were either naff, not as good as the one it was replacing or such. It happened a lot with flasher relays and bearings.
I can test the sender I took out when I get a moment - I should have tested the replacemnt in retrospect.
I still wonder if the motor is running cold though.
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peteinchad
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Location: UK
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| Posted: Sun May 17, 2015 19:42 Post subject: |
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I doubt it is running cold - I was sure mine was but I was wrong.
If you have jump leads then just try putting one end of the lead onto the body of the sender and the other end to the earth terminal on the battery - just to rule out bad earth connection on the sender threads. |
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helijohn
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Joined: 24 Nov 2003
Posts: 2612
Location: Seaside resort
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| Posted: Sun May 17, 2015 20:20 Post subject: |
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| peteinchad wrote: |
I doubt it is running cold - I was sure mine was but I was wrong.
If you have jump leads then just try putting one end of the lead onto the body of the sender and the other end to the earth terminal on the battery - just to rule out bad earth connection on the sender threads. |
Yeah, it certainly gets hot at the rad's header!
I'll have to give the 'earth' approach a try when I next run the car to temperature. I did run a lead from it to the -ve on the battery but it might have needed better and croc. clamps sound like a good idea.  |
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helijohn
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Joined: 24 Nov 2003
Posts: 2612
Location: Seaside resort
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| Posted: Sun May 17, 2015 23:45 Post subject: |
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| peteinchad wrote: |
I fitted an extra gauge and when it showed me my engine wasn't running too cold then I changed the original sender only because I don't like things that don't work properly. |
Where did you insert the sender for the aftermarket gauge?? |
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peteinchad
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| Posted: Mon May 18, 2015 4:38 Post subject: |
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I did mine differently to most other people and used a thermocouple probe bolted to the head itself.
Most people put it into the top hose using an adapter like THIS
Don't forget to earth it though as the top hose will insulate it from the car. |
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helijohn
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Joined: 24 Nov 2003
Posts: 2612
Location: Seaside resort
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| Posted: Mon May 18, 2015 9:02 Post subject: |
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| peteinchad wrote: |
I did mine differently to most other people and used a thermocouple probe bolted to the head itself.
Most people put it into the top hose using an adapter like THIS
Don't forget to earth it though as the top hose will insulate it from the car. |
I looked at those but I didn't want to cut into the hose as hoses are not that easy to get if I needed one. It's 2 weeks from a Mitsy dealer and 10 days from Japan or the UAE. Can I pick your brains about the head thermocouple. When I ran an electric fan on my SJ it had a probe to go under the hose but I strapped it to the rad header instead. It worked cos the sender was attached to a variable control and I could set it to come on at the right temp; this is not an option really for a temp gauge. I would prefer something like that again. |
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Simon_W
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Joined: 21 May 2013
Posts: 4881
Location: Watford
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| Posted: Mon May 18, 2015 10:13 Post subject: |
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| helijohn wrote: |
| I looked at those but I didn't want to cut into the hose as hoses are not that easy to get if I needed one. |
I share your dislike for cutting hoses, but in fact you won't make the hose any more likely to fail if you put a coupling for a sender in it. I fitted one a few months ago and it's given no problems at all. Just make sure that, if you do, you insert it in a straight section of the hose so that it's not under any stress. |
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helijohn
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Posts: 2612
Location: Seaside resort
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| Posted: Mon May 18, 2015 10:55 Post subject: |
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| Simon_W wrote: |
| helijohn wrote: |
| I looked at those but I didn't want to cut into the hose as hoses are not that easy to get if I needed one. |
I share your dislike for cutting hoses, but in fact you won't make the hose any more likely to fail if you put a coupling for a sender in it. I fitted one a few months ago and it's given no problems at all. Just make sure that, if you do, you insert it in a straight section of the hose so that it's not under any stress. |
Lol - such a small hose there is not much straight.
I just tested the old sender and to my mind it is working OK. Cold the resistance is 0.9 and in boiling water it drops to 0.13.
The 0.9 possibly explains why the gauge moved up a little when powered. The 0.9 tells me the resistance is pretty much nowt - the gauge at that should be registering overheating I think!!  |
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helijohn
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Posts: 2612
Location: Seaside resort
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| Posted: Mon May 18, 2015 11:04 Post subject: |
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| I meant to add (but couldn't as there is no 'edit' Arghhhhhh) it is starting to look like a gauge fault. |
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Simon_W
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Joined: 21 May 2013
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Location: Watford
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| Posted: Mon May 18, 2015 11:15 Post subject: |
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| helijohn wrote: |
| I meant to add (but couldn't as there is no 'edit' Arghhhhhh) it is starting to look like a gauge fault. |
I agree that the sender would seem OK. The figures you posted (I assume kΩ) are pretty much in line with the sender on my Challenger. I measured approx 0.9kΩ at 40 °C, and 0.13kΩ at 100 °C. |
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peteinchad
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Joined: 07 Jan 2013
Posts: 15079
Location: UK
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| Posted: Mon May 18, 2015 11:37 Post subject: |
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| helijohn wrote: |
| it is starting to look like a gauge fault. |
The gauge moves full scale when you earth the wire though. |
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peteinchad
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Posts: 15079
Location: UK
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| Posted: Mon May 18, 2015 11:44 Post subject: |
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| helijohn wrote: |
Can I pick your brains about the head thermocouple. |
I did a write-up of it HERE
It gives different readings to the ones that read the water temperature because it is measuring the temperature of the metal of the head.
It takes a while to work out what is "normal" for your engine - mine is 62oC - which is less than what the other type of gauge reads. But once you know then it isn't a problem. |
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helijohn
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Joined: 24 Nov 2003
Posts: 2612
Location: Seaside resort
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| Posted: Mon May 18, 2015 12:11 Post subject: |
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| peteinchad wrote: |
| helijohn wrote: |
| it is starting to look like a gauge fault. |
The gauge moves full scale when you earth the wire though. |
Yes it does but I recall in my motors of bygone years that the gauge would creep (quickly even so) to full scale when earthed out. This flicked right up violently and I was not expecting that. I might fit a pot to an earth wire and see if I can simulate the sender.
Excellent write up on the head mounted temp gauge. 
I think I am going to get myself a cheap gauge and see what I can do with it and its sender. I have already fitted a voltmeter - I like one in every car - so I'll fit an accessory temp gauge to match. |
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